OC is Over Crank. It means that the controller is sensing that the engine is cranking too long, and not starting.

But if the engine is not even cranking, this is the problem.

The first thing you need to do is to take the battery and have it load tested. Do not rely on a voltmeter to test the battery, as even a bad battery can read fully charged, but not have enough ampacity to do any work.

IF the battery is bad, replace it.

if the battery tests good, you will need to remove the controller.

Udnerneath the controller is a relay. This is the start relay.

On pin 30, wire 14P, test the voltage. How much voltage does it read?

At pin 86, wire 71, test the voltage while setting the switch to MANUAL. What voltage o you read there?